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Free keywords:
Astrophysics, High Energy Astrophysical Phenomena, astro-ph.HE
MPINP:
HESS - Abteilung Hofmann
Abstract:
A hotspot at a position compatible with the BL Lac object 1ES 2322-409 was
serendipitously detected with H.E.S.S. during observations performed in 2004
and 2006 on the blazar PKS 2316-423. Additional data on 1ES 2322-409 were taken
in 2011 and 2012, leading to a total live-time of 22.3h. Point-like
very-high-energy (VHE; E>100GeV) $\gamma$-ray emission is detected from a
source centred on the 1ES 2322-409 position, with an excess of 116.7 events at
a significance of 6.0$\sigma$. The average VHE $\gamma$-ray spectrum is well
described with a power law with a photon index
$\Gamma=3.40\pm0.66_{\text{stat}}\pm0.20_{\text{sys}}$ and an integral flux
$\Phi(E>200GeV) = (3.11\pm0.71_{\rm stat}\pm0.62_{\rm sys})\times10^{-12}
cm^{-2} s^{-1}$, which corresponds to 1.1$\%$ of the Crab nebula flux above 200
GeV. Multi-wavelength data obtained with Fermi LAT, Swift XRT and UVOT, RXTE
PCA, ATOM, and additional data from WISE, GROND and Catalina, are also used to
characterise the broad-band non-thermal emission of 1ES 2322-409. The
multi-wavelength behaviour indicates day-scale variability. Swift UVOT and XRT
data show strong variability at longer scales. A spectral energy distribution
(SED) is built from contemporaneous observations obtained around a high state
identified in Swift data. A modelling of the SED is performed with a stationary
homogeneous one-zone synchrotron-self-Compton (SSC) leptonic model. The
redshift of the source being unknown, two plausible values were tested for the
modelling. A systematic scan of the model parameters space is performed,
resulting in a well-constrained combination of values providing a good
description of the broad-band behaviour of 1ES 2322-409.
